Characterization of a novel human T cell receptor β chain variable region family by transspecies DNA hybridization

One essential component in the generation of diversity of T cell receptor (TcR) α and β chains is the existence of multiple tandemly arranged variable regions in the germ line which are subsequently rearranged to form functional units. In attempting to establish the extent of the human TcR α and β chain repertoire an approach of randomly sequencing cDNA for rearranged receptors has been generally pursued. So far, 24 human Vβ families have been characterized and they encompass some 51 transcriptionally active gene segments. Recently, surveys of several hundred TcR β cDNA clones have failed to establish further Vβ families which suggests that if they exist, they are likely to be poorly represented in the peripheral blood repertoire. It is likely, therefore, that the majority of human Vβ regions which are rearranged conventionally and are transcriptionally active have already been described. To investigate whether additional Vβ families characterize the human TcR repertoire we have examined Vβ sequences from an inverse polymerase chain reaction (PCR) TcR β cDNA library of the chimpanzee, the most closely related creature to man. One clone which could not be assigned to any human Vβ family cross‐hybridized with human TcR β chain cDNA. This new human family has been called Vβ25. Comparison of chimpanzee and human Vβ25 sequences using the Lipman‐Pearson method gives a similarity index of 94.6% over a consensus length of 112 amino acids. On the evidence of Southern blotting with cDNA probes, Vβ25 segments in human and chimpanzee appear to represent single member gene families and no restriction fragment length polymorphism was evident with the restriction enzymes used. Equalization of TcR β cDNA followed by family‐specific quantitative PCR showed that the gene is expressed at similar levels in the chimpanzee and the human. The actual level of expression in the human is less that 0.5% of the total TcR β repertoire. Transspecies DNA hybridization using novel sequences from closely related species may be a powerful tool for establishing the full extent of TcR α and β and immunoglobulin repertoires.